Non-standard splines

[rharr]

I'm trying to draw a hub and shaft to look at the quality of fit and can't seem to find calculations for non-standard splines.
The shop making the hub told me they are cutting a 24 tooth spline with a 7/9 diametral pitch and a 27.5 degree pressure angle. Yes. That is correct. That's what I was told.
The shaft has a 24 tooth Grob spline with a nominal diameter of 3.250" and a chord of 1.021".
Any help will be appreciated.
Thanks.

 

[dimjim]

Your chordal dimension really looks strange.
Is this a span measurement over two teeth?

 

[rharr]

I know the equations for Grob splines typically have the chord over two teeth. If you rotate (polar array) a set of parallel lines 1.021" apart about a center you end up with this being over three teeth. This specification is on several prints around here and goes back 20 years or so. I can only assume it works. However, I've found other errors on prints we've reproduced time and time again. Sometimes our vendors just make it work regardless of the data on the print.
If I had the data on the mating hub, I could be more sure.

 

[gearcutter]

Wow!
This is one I've never come across.
To work it out I'm going to need more information.
Can you get hold of data for both hub & shaft such as: major & minor diameters, fillet radii of internal & external cutters, measurments with pins, required clearance/fit and the amount of profile shifts.
Also, can you confirm the span dimension over 3 teeth by measuring the shaft? If so, what are span measurments taken over 2 teeth and 4 teeth?

 

[rharr]

All the shaft information I have is:
Grob spline with 24 teeth
3.250 nominal diameter
3.362/3.358 major diameter
3.140/3.125 minor diameter
.015 root radius
1.022/1.020 chord

And I have less on the hub. Over the telephone I was told, "involute spline with twenty four teeth, seven nine diametral pitch, and a twenty seven and a half degree pressure angle. And, the hub has a minor diameter of 3.150/3.155."

This is the part I'm having trouble with. All the formulas and tables I've found for involute spines are for 30, 37.5, and 45 degree pressure angles and are for standard types where the stub pitch (denominator) is twice the diametral pitch (numerator).

As for trying to confirm any dimensions on the shaft, all I have is a worn shaft to look at and 1.021 over three teeth looks like it's what it might have been new. Trying to get the span over two or four teeth would only be a guess as over half of each tooth is worn away.

I know the shaft and hub, as described above, are not intended to work together. I'm trying to see just how bad the fit is.

 

[gearcutter]

I don't mind that the shaft is worn. I need the actual BTL measurments over 2, 3 & 4 teeth. These will give me the info I need to work out the base pitch which should then confirm the pitch and pressure angle.

 

[rharr]

By BTL do you mean base tooth length?
At the base, which is all that's left on one side of the teeth, I measure .625 across 2 teeth and 1.400 across 4 teeth.

 

[gearcutter]

Does this look anything like the shaft? Based on your dimensions this is the best I can come up with. While it is 7Dp it doesn't work out to a tooth depth for 9Dp, I suggest something maybe incorrect with this spec. It seems to work out closer to 7/14 Dp with, as you can see, a large minus addendum correction.

Number of teeth 24
Normal module 3.6286
Pressure angle at normal section 27.5000
Dedendum reference profile (module) 0.268
Tooth root radius Refer profile (module) 0.10
Addendum Reference profile (module) 0.508
Addendum modification coefficient -0.7416
Reference diameter (mm) 87.086
Major diameter (mm) 85.390
Minor diameter (mm) 79.760
No of teeth over which to measure 4
Base tangent length 36.041
Pin diameter (mm) 6.500
Dimension over two rolls (upper) 91.204
Chordal tooth thickness 2.898
Reference chordal height (mm) -0.826

 

[rharr]

Interesting that you were able to come close to the Grob spline on the shaft with an involute style. This is probably what the hub manufacturer did. They took measurements off the shaft, assuming it was an involute spline, and made a hub based on those measurements.

How would I adjust these dimensions for the mating hub?

And, what about the 7/9 Dp? How does one generate the rest of the specification based on this and the 27.5 degree pressure angle?

Is there any way for me to paste this image into an AutoCAD file as anything but a picture?

 

[plasgears]

I had a design in which the spline was generated at assy. It worked fine in a high torque application.

The gear is hardened PM with an internal spline. The shaft is not hardened, and the the gear is pressed on the shaft thus generating an intimate spline. The spline shape can be anything you desire, preferably shallow.

 

[gearcutter]

Follow this link and send me an email with your contact details. I can then send you a DXF of the internal/external profiles.

http://www.aussieweb.com.au/email.aspx?id=1194181